In the following, medium-voltage cables refer to cables that are used in the voltage range of 12-36 kV, and high-voltage cables refer to cables that are used in the voltage range exceeding 36 kV.
When jointing cable, the conductors from two cable ends are joined together with a jointing sleeve after the respective conductor has first been exposed from the surrounding insulation. The joint with the jointing sleeve must then be insulated. This insulation is usually carried out with a pre-fabricated jointing body of rubber. Known jointing bodies are usually formed with a substantially cylinder-shaped shell. The actual jointing body is provided with a continuous cylindrical hole, where the hole in the natural, non-stretched, state has an inner diameter that is somewhat smaller than the outer diameter of the insulation on the cable to be jointed. This is necessary for the elastic jointing body after the jointing to embrace the insulation of the cable ends for the purpose of obtaining a close-fitting joint.
When jointing is to be carried out, the work is initiated by placing the jointing body in a rest position over one of the cable cores. The cable ends are prepared by exposing the conductor cores from the insulation and joining the conductor ends together. The joining is usually carried out with a jointing sleeve which by means of mechanical deformation brings the sleeve into contact with the conductors. Thereafter, the jointing body is brought to a centred position over the jointing sleeve.
Elastically expandable adapters are used to adapt a cable joint or a stress cone, with an inner diameter adapted to a certain cable diameter, to a cable with a smaller cable diameter. By using adapters, a cable joint or a stress cone may be used for a plurality of different cable diameters. A stress cone is used in a cable joint or a cable termination.
Moving a jointing body over a cable without first stretching the jointing body is difficult and allows the jointing body to be used only on a cable with a well-defined outer diameter that is adapted to the size of the jointing body. It is therefore common for the jointing body to be stretched onto a tube before the jointing body is brought into place, first over one cable core and thereafter over the joint with a jointing sleeve.
It is known to stretch the jointing body onto a thin tube even at the factory. The jointing body with the tube then has an inner diameter that is larger than both the outer diameter of the cable that is jointed and a possible jointing sleeve in the joint, whereupon the jointing body may be easily fitted onto the cable according to the above. It is also known, when jointing power cables in the field, to stretch the jointing body onto a tube in connection with the jointing to be carried out.
Irrespective of where the stretching of the jointing body occurs, there is a need to facilitate the application of an elastically expandable body onto a stiff tube.